TiddlyWiki - a non-linear personal web notebook
Scribbleton - The little personal wiki.
Zim Wiki - Zim is a graphical text editor used to maintain a collection of wiki pages. Each page can contain links to other pages, simple formatting and images.
Banana Dance Wiki/CMS - Free open source software combining the best of wiki and CMS with community building-features.
ZuluPad - ZuluPad is a notepad on crack.
DokuWiki - DokuWiki is a simple to use and highly versatile Open Source wiki software that doesn't require a database.